Endless rubber tracks are increasingly being used for propelling various vehicles over the ground such as, for example, various tractors and other agricultural vehicles including, for example, combines and spreaders, as well as various earth moving machines.
For the vehicle, such rubber track is conventionally positioned over at least two vehicular wheels, normally a drive wheel for engaging an inner surface of the rubber track and driving the track and at least one vehicular driven wheel to aid in guiding the contorted path of the rubber track as it moves around the vehicular wheels to propel the associated vehicle over the ground.
The outer surface of the rubber track, namely its tread, is intended to be ground contacting and typically contains a plurality of raised rubber lugs designed to contact, or engage, the ground.
The inner surface of the track typically contains a plurality of spaced-apart relatively hard rubber lugs which normally serve as guide lugs and which, for some vehicular drive wheel configurations, may also serve as drive lugs to be driven by the associated vehicular drive wheel and such lugs are generally referred to herein as guide lugs even if they are utilized as positively driven drive lugs.
The hard rubber guide lugs serve to guide the rubber track around the aforesaid vehicular drive wheel and guide wheels. In such case, the vehicular drive wheel typically drives the track by its friction against the inner surface of the track. It might sometimes be referred to as a friction drive, or friction driven track. Such hard rubber lugs positioned on the inner surface of the track are referred to herein as guide lugs.
As discussed above, the vehicular drive wheel may be designed to actually engage the hard rubber lugs to drive the track and thereby propel the associated vehicle over the ground. Such hard rubber lugs may sometimes be used as drive lugs, although they also serve as guide lugs and are therefore simply referred to herein as guide lugs.
Where the guide lugs for the track are of a relatively hard rubber and where the surface of the track onto which they are positioned are of a somewhat softer rubber, imitation and propagation of cracks in the rubber surface of the track between the hard rubber lugs may potentially occur. In particular, as the rubber track is driven around the aforesaid vehicular wheels, it is subject to extensive contorted flexing and, therefore its guide hard rubber lugs are subject to potential crack initiation and propagation at a juncture region on the rubber surface of the track where such lugs join the rubber track.
Accordingly, it is desired that the region of the inner surface of the track which joins the hard rubber guide lugs are somewhat softer yet still have an appropriate resistance to flex fatigue, resistance to tearing and resistance to crack propagation.
In the description of the invention, the term “phr” relates to parts by weight of a particular ingredient per 100 parts by weight of rubber contained in a rubber composition.
The terms “rubber” and “elastomer” are used interchangeably unless otherwise indicated. And the terms “cure” and vulcanize” may be used interchangeably unless otherwise indicated.